Transcript nervous system A

Nervous System
and Senses
Neural Activity
The Neuron
• Which direction does a
signal travel down a
neuron?
• What do you think a
“signal” is?
• How do you think the
neuron controls where
the signal goes next?
Electrical Events
• An action potential is
an “all or nothing”
event. A neuron
either sends a signal
or it doesn’t.
• Relative strength or
weakness of a signal
come from frequency,
not size of the
potential.
Resting potential
• Using active
transport, the
neuron moves N+
ions to the outside
of the cell and K+
ions to the inside of
the cell.
• Large molecules in
the cell maintain a
negative charge.
Action potential
• On receiving a
stimulus, sodium
gates and potassium
channels open briefly,
allowing these ions to
diffuse.
• The gates close, and
active transport
restores the resting
potential.
Traveling Potentials
Traveling Potentials
Synapse
• A gap called a
synapse controls
the transmission of
signals.
• Neurotransmitters
cross the synapse
and stimulate the
next neuron.
Some Neurotransmitters
Neurotransmitter
Location
Some Functions
Acetylcholine
Neuron-to-muscle synapse
Activates muscles
Dopamine
Mid-brain
Control of movement
Epinephrine
Sympathetic system
Stress response
Serotonin
Midbrain, pons, medulla
Mood, sleep
Endorphins
Brain, spine
Mood, pain reduction
Nitric oxide
Brain
Memory storage
During resting potential, which
channels are closed?
25%
1.
2.
3.
4.
25%
25%
25%
Potassium
Sodium
All
None
1
2
3
4
What determines the intensity of a
neural signal?
1. Speed of action
potential.
2. Size of action
potential.
3. Duration of action
potential.
4. Frequency of action
potentials.
25%
1
25%
2
25%
3
25%
4
During a resting potential, where are most
positively-charged particles found?
33%
33%
33%
1. Outside the neuron.
2. Inside the neuron.
3. Equal amounts are
found on both sides
of the membrane.
1
2
3
• Sketch a neuron and label the four major
parts.
• Diagram a synapse and show how action
potentials travel from one neuron to the
next.
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Information Processing
Why a CNS?
• Neurons control movement. The brain
(or spine) interprets sensory signals and
determines the appropriate movements
(that is, behavior).
• Appropriate movement is critical to the
survival of most animal species.
• Selection has favored a central nervous
system to control responses.
Four basic operations
• Determine type of stimulus
• Signal the intensity of a stimulus
• Integrate responses from many sources
• Initiate and direct operations
Type of stimulus
• How does the brain “know” if a sensory
signal is visual, auditory, etc.?
• Areas of the brain dedicated to specific
sensory signals are connected to nerves
that connect to specific sensory organs.
• “Cross-sensory” effects: a poke in the
eye produces stimulates the optic nerve,
producing visual effects.
Intensity of stimulus
• Intensity =
frequency of
action potentials
Integration of stimuli
• Convergence = Signals may arrive
through many neurons, but may all pass
their signal to a single connecting
neuron.
• Such cells may be “decision-making”
association neurons that may determine
an appropriate output.
Directing operations
• Neural pathways consist of:
• Sensory neurons
• Association neurons, which receive
signals from many sources
• Motor neurons
• Effectors: muscles, glands
Reflexes
• The simplest neural pathway is the reflex arc.
• This involves one or more sensory neurons,
association neurons in the spine, and motor
neurons, which carry out the reflex entirely
before the brain is aware of the response.
Reflex Arc
What is the effector in the familiar
knee jerk reflex?
1. The knee hammer
2. Sensory receptors in
the patellar tendon
3. Sensory neurons
running up the leg
4. Motor neurons
running down the leg
5. The quadriceps
muscles
20%
1
20%
20%
2
3
20%
4
20%
5
• You’re probably all familiar with the kneejerk reflex, which your doctor uses to test
your reflexes. Sketch a reflex arc for the
knee jerk reflex, beginning with whacking
your knee with a hammer. Label the
sensor and effector in your diagram.
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Organization
Neural organization
Central Nervous System
• Consists of brain and spine
• Functions:
• Receives sensory signals
and determines
appropriate response
• Stores memory
• Carries out thought
Spine: structure
• The spinal cord is
protected by the
vertebrae.
• Gray matter contains
cell bodies; white
matter contains
myelinated fibers.
• PNS nerves extend
outside of the
vertebrae.
Brain: Structure
• Hindbrain carries
out the most basic
functions.
• Midbrain
coordinates signals.
• Forebrain
processes signals,
stores memories,
creates thought.
Peripheral nervous system
• Nerves, neurons, and sensory organs
outside the central nervous system
• Functions:
• Sends signals to the CNS
• Receives and transmits
motor signals from
the CNS
• Stimulates effectors
Somatic nervous system
• Motor neurons that control
voluntary movements by
activating skeletal muscles.
• Also involved in what we
perceive as involuntary
movements, such as reflexes
(though voluntary control of
the muscles involved, such
as tensing them, can reduce
the response).
Autonomic Nervous System
• Motor neurons that
control involuntary
responses involving
the organs, glands,
and smooth
muscles.
Sympathetic division
• Portion of the autonomic
nervous system that produces
the “fight or flight” response:
• Dilation of pupils
• Increased heart and
breathing rates
• Constriction of blood
vessels
• Inhibits digestion
Parasympathetic Division
• Portion of the autonomic
nervous system that
produces the “rest and
ruminate” response:
• Constricts pupils
• Dilates blood vessels
• Reduces heart and
breathing rates.
• Stimulates digestion.
The central nervous system
includes:
25%
25%
25%
25%
1. Brain only
2. Brain and spine
3. Brain, spine, and
major nerves
4. Spine and major
nerves
1
2
3
4
Motor neurons carry signals which
direction?
25%
25%
25%
25%
1. Sensory organs ->
CNS
2. Muscles -> CNS
3. CNS -> sensory
organs
4. CNS -> muscles
1
2
3
4
Which activity is most likely to activate the
sympathetic division of your nervous
system?
25%
25%
25%
25%
1. Cuddling kittens
2. Watching an exciting
action movie.
3. Meditating
4. Lying in the sun
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